39 



In the second place, when water is applied to a sandy soil, not 

 nearly as much remains adhering to the surface of the soil grains and 

 entangled between them, so that it quickly spreads downward farther 

 below the surface than is the case with the clay. This being true, it 

 takes less water to produce effective drainage, and the roots of the 

 crop spreading farther in the sands, the salts cannot beoome concen- 

 trated as they may in the clays. 



In the third place, since more water is held in contact with the soil 

 grains of the clays, and since the total surface for chemical action to 

 take place upon is very much larger in the clayey soils than in the 

 sands, it is plain that soluble salts, including alkalies, may form more 

 rapidly in one case than in the other, and hence, that the open, sandy 

 soils cannot become alkali lands except under conditions which are 

 extremely favourable to their formation. . 



DRAINAGE THE ULTIMATE REMEDY FOR ALKALI LANDS. 



If it is true that alkali salts are formed from the decomposition of 

 the soil and subsoil through the action of water and air, it is only too 

 plain that where conditions are persistently maintained which allow 

 the formation of the salts without permitting them to be removed by 

 any cause whatsoever, there must come a time, sooner or later, when 

 the amounts produced and accumulated in the soil shall reach the 

 degree of concentration which is intolerable to cultivated crops. 



Under the natural conditions of rainy countries, there is usually a 

 sufficient amount of leaching to permit the white and black alkalies to 

 be borne away in the country drainage with sufficient completeness to 

 prevent their effects attracting general attention, and if the same pro- 

 cesses obtained in irrigated countries it is plain that in these, too, the 

 difficulties would not arise. 



The conclusion is irresistible, therefore, that some method must be 

 devised by which, periodically at least, sufficient water is applied to 

 irrigated fields to pick up and carry out of the country the soluble 

 alkali salts which are fatal to cultivated crops. 



In the old-time irrigation of the Nile valley, the greater part of the 

 land was under basin irrigation and thus thoroughly washed during 

 some fifty days every year. Lands not 60 treated were the lighter 

 sandy soils near the Nile, protected by only slight bariks from inunda- 

 tion, and these dykes usually gave way as often as every seven or 

 eight years, so that they, too, were occasionally thoroughly flooded. 

 Under this system of washing and drainage the fields of the Nile were 

 kept free from alkalies for thousands of years. But at the present 

 time, when what are called more rational methods are being applied, 

 but with no attention being paid to treeing the soil from the accumu- 

 lation of alkalies, these salts have been concentrated to so serious an 

 extent that already many acres have been abandoned. The probabili- 

 ties are that long, long ago the same more rational methods (?) now 

 being practised had been tried and found inadequate or inapplicable, 

 on account of the accumulation of alkalies which they permitted, and 

 the old irrigators learned to be content with a system which, although 

 more wasteful in some ways, still kept the dreaded alkalies under con- 

 trol It is not improbable that if the full history of many abandoned 

 ancient irrigation systems could be known, it would be found that not 

 being able to command water sufficient for drainage, or not apprecia- 



